1. Field of the Invention
The present invention relates to a circuit interrupter for performing the arc extinction by puffing a fluid for arc extinction such as SF.sub.6 gas. More particularly, it relates to a self-arc extinction type circuit interrupter in which high pressure fluid whose pressure is raised by an arc formed between contacts is used for performing the arc extinction.
2. Description of the Prior Arts
In the conventional circuit interrupters, a fluid having high arc extinct property is used and the fluid is puffed to the arc so as to diffuse and to cool the arc in order to improve the arc extinct function.
It has been proposed to employ the puffer system actuating a puffer device while interlocking to the interrupting operation; or the double pressure system maintaining high pressure source by a compressure in the normal state and opening a valve while under interlocking to the interrupting operation in order to give high puffing effect.
Thus, the puffer system requires large power for the operation because the puffer device is mechanically operated while interlocking to the interrupting operation. However, the puffer device requires large power for the arc extinction and the required power is increased depending upon the arc current whereby the operating device should be large size and the strength of the transmitting mechanism should be high. Moreover, in the interruption under no load or small arc current as main operations, the puffer load is quite small. In the mechanism having high operating power, excess operating power is caused to accelerate in abnormal condition whereby excess puffer action is given for the interrupting current and remarkable current interrupting is caused in a large capacity type apparatus and the abnormal voltage is generated. There are various disadvantages from the practical and economical viewpoints.
In the double pressure system, the double pressure system structure, the attachment such as a valve and a compressor and the control devices thereof are needed to cause the disadvantage of the larger size and the complicated structure.
In order to overcome the disadvantage of the conventional apparatus, it has been proposed to employ a new system in which a high pressure source is formed by the pressure raising effect of the arc mainly the heat energy thereof and the high pressure fluid is puffed to the arc space during the time decreasing the arc current to zero to perform the arc extinction.
In the self-arc extinction type interrupter, the pressure of the gas in the arc extinct chamber containing the contactors is raised by the arc energy given through the gas for arc extinction and the arc and the high pressure gas is stored in a chamber having suitable volume and the high pressure gas in the chamber is discharged to the arc space depending upon the sudden pressure drop in the arc during the time decreasing the arc current or the release or elimination of the closing function thereof, whereby the gas flow is maintained for suitable time to perform the arc extinction.
In these interrupters, in order to effectively raise the pressure of the gas for arc extinction, a fixed contact and a movable contact are disposed in the arc extinct chamber which is in substantially closed condition and an outlet disposed at the lower end of the arc extinct chamber is substantially closed by the movable contact at the time departing the contacts, and the nozzle for discharge is formed after passing the movable contact through the outlet during the interrupting operation.
In the system, the high pressure source is mainly formed by the heat energy whereby the high pressure fluid is heated at high temperature.
When the fluid for arc extinction is heated to high temperature, the density of the fluid is minimized which accelerates the ionization and decreases the insulation and the diffusion effect and the cooling effect whereby the arc extinct effect is not highly decreased.
In the phenomenon, the temperature is raised depending upon increasing the pressure raising effect to raise the pressure and to improve the function, whereby the conductivity is remarkably increased to decrease the arc extinct effect. As the result, the effect is limited and it is difficult to prepare a device having large capacity.
Even though the interrupting current is large and the pressure in the arc extinct chamber is enough to perform the arc extinction in these structures, the pressure in the arc extinct chamber is raised to the abnormal state until passing the movable contact through the outlet to form the nozzle. Moreover, the arc is expanded too much whereby it is necessary to use the material having high mechanical strength as the parts of the arc extinct chamber and to have the complicated structure. Moreover, since the consumption of the contact is large, the exchange of the contact should be frequent and the practical function is inferior disadvantageously.
When the position of the opening part of the outlet is decided so as to fit to the large current interruption, it is not easy to give high pressure in the arc extinct chamber in the small current interruption. For example, when the recovery voltage after the interruption is remarkably high as in the case of switching a capacitor bank, the interrupting effect is inferior.
The maintenance of the pressure is important in both the direct system and the indirect system. In the conventional direct system, the structure is simple and economical, however, the temperature of the fluid in the arc extinct chamber is raised because the fluid heated in the arc space is charged for raising the pressure in the arc extinct chamber. Accordingly, the density of the fluid, the diffusion effect, the cooling effect and the insulation are decreased whereby the arc extinct effect is inferior disadvantageously.
When the interrupting current is large and a remarkably large amount of energy is fed into the arc space, if all of the energy is used as the source for raising the pressure, the pressure of the fluid for arc extinction is remarkably raised and the arc voltage is increased and the arc energy is increased and the fluid filled in the arc space is further heated to result the fluid at high temperature whereby the pressure is further raised.
When the fluid for arc extinction is heated to high temperature, the insulation is usually lost to result in an increase of the electric conductivity and the insulation recovery is inferior. Moreover, the density of the fluid is decreased and the diffusion of the energy in the arc space is low and the rapid cooling of the fluid heated to high temperature is not easily attained. Accordingly, it has been difficult to improve the function and to increase the capacity in the conventional apparatus.
Moreover, in the conventional apparatus, the mechanism for raising the pressure mainly relies on the direct heating by the arc whereby the heating effect is given for raising the pressure and the temperature of the fluid in the space is raised. The high temperature of the fluid causes the decrease of the density and the ionization is promoted by the thermal ionization, and the diffusion and cooling effects are remarkably decreased and the arc extinct effect is decreased. Accordingly, it is preferable to form the high pressure fluid and to cool the high pressure fluid.
Incidentally the high pressure fluid is obtained mainly dependent on the high temperature. However, the arc itself is movable and has irregular form and the condition of the arc can be varied at relatively high speed depending upon the environmental condition. Accordingly, the fluid whose pressure is raised by the irregular arc causes the turbulent condition and the fluid is not smoothly flowed under the pressure releasing condition and the arc extinct effect is unstable in comparison with the outer operation system such as the puffer system.
In order to improve the interrupting effect in the case of a small interrupting current and slowly raising the pressure in the arc extinct chamber, it is necessary to prolong the closing time for passing the movable contact through the outlet.
In order to improve the interrupting function in the case of large interrupting current, the outlet is rapidly opened to prevent excess raising of the pressure in the arc extinct chamber whereby the damage of the parts and the abnormal consumption of the contact should be prevented.
Moreover, when the operation of the movable contact is affected by the variation of the interrupting current, to vary the pressure and to cause electromagnetic acceleration, the timing for opening and closing the outlet is further varied. Accordingly, it is difficult to obtain a circuit interrupter which has practically stable interrupting effect in a wide range from large current to small current.
When the pressure is raised too much in these systems, the arc space is heated to high temperature to raise the temperature of the fluid even though it should impart low temperature and high pressure on the spaces. Accordingly, the thermal dissociation of the fluid in the space is caused and many ionized particles are introduced to remarkably decrease the arc extinct effect, and it is difficult to practically use it.
It is necessary to prevent the decrease of the arc extinct effect by resulting the condition of low temperature and high pressure in the space for the high pressure source and to control the increase of the thermal dissociation i.e. the increase of ion density, in these systems. However, in the self-arc extinction type apparatus, the temperature of the fluid in the space as the high pressure source, is raised in each interrupting operation with the residual heat energy. When the interruption is repeated for a short time, the fluid at high temperature is accumulated to decrease the arc extinct effect.
In the structure having plural spaces as the high pressure source, the residual heat energy is highly remained at the upper space.
In a single space, the fluid at high temperature remained at the upper part of the space because of buoyancy resulted by decreasing the density of the fluid.
In the self-arc extinction type, the pressure raising is an important factor. However, the pressure raising mechanism mainly relies on the heat energy of the arc. Accordingly, the heat transfer is caused by raising the pressure to raise the temperature of the fluid in the space at high degree. The arc extinct effect at the pressure releasing is decreased by the raising of the temperature. When the temperature is raised over a specific level, the arc extinct level is substantially lost. Accordingly, it is necessary to consider the heat energy problem as well as the pressure problem.
When the pressure is raised too high, the arc space and the high pressure fluid for the arc extinction are heated to high temperature. When the fluid is heated over a specific level, the decrease of density and the ionization formed by the thermal dissociation are rapidly caused whereby the arc extinct effect is remarkably decreased.